This invention relates to intaglio printing process and, more particularly to a process for printing bank notes, postage stamps, bonds and securities, which are prevented from forgery or counterfeit and provided with novel appearance and rich gradations.
The intaglio printing process in accordance with the present invention employs a printing plate consisting of a precise engraving element which is adapted from a gravure printing plate. This printing plate applied on the plate cylinder is printed with very stiff and viscous ink as used for engraving intaglio printing. Ink of various colors may be applied separately on different portions of the gravure plate surface by rollers. After inking, surplus ink can be wiped off by wiping roller. Printing paper may be introduced between the plate cylinder and impression cylinder for printing.
Bank notes, postage stamps, bonds and securities can represent a huge value of money on one sheet of paper. Therefore, these securities must be printed with great care so that they will not be forged or counterfeited. To attain this object, considerable efforts have been made for the selection of paper quality, application of water mark, or special preparation of printing ink. In addition, very complicated patterns and lines, as well as various images and colors were used for displaying precise representations on the paper. Particular identification marks or numbers were also applied on the paper sheet to prevent forgery and counterfeiting.
For the manufacture of papers of the character as described above, it has been a usual practice to use the process of engraving intaglio rotary printing.
The printing plate used for this process has been provided with engraving by manually skilled craftsman with a highly artistic sense and furnished with geometrical patterns or designs produced by elaborate engraving machines paying due attention to the requisite of preventing forgery and they have made great endeavors even to obtain a single printing plate. In the course of the printing, it has been common to use ink of several kinds of color which is stiff and viscous to be applied on the surface of the printing plate. Such printing process provides an artistic and effective printed paper for the prevention of forgery by dint of variation of width and depth of engraving lines on the printing plate. Due to representation by engraved drawing lines, however, it had a disadvantage that the printed image often became quite monotonous. Thus, photographically fine representation or continuous gradations were not satisfactorily obtained by this process.
Among these securities, the postage stamp has mostly used gravure printing. By use of several kinds of gravure plates and colors, gravure printing could offer a large number and varied kinds of fine postage stamps rapidly. According to this gravure printing, the printing was made by use of a usual gravure printing machine. The printing plate for this purpose was normally formed of small recesses or cells sectioned by gravure screens and having different depths on the printing plate. Printing ink could fill in these cells and produce fine gradations of colors in highlight or shadow continuously on the printed paper. This ink is generally termed as gravure ink. It is soft and fluid, containing much evaporating solvent and is low in viscosity. Thus, the gravure ink was applied to the cells of the printing plate. In a subsequent step of the process, the surplus ink which remained on the gravure printing plate was scraped off by a doctor blade.
Since the gravure printing process uses a very fluid ink which readily flows downwards, it is impossible to use for one-plate multiple color printing. The fluid ink then used is so soft as to flow freely downwards because it contains much evaporating solvent. It is caused by this fluidity that a phenomenon appears as described below in the cells of different depth on the gravure plate. This gravure plate is provided with a number of cells as above described. These cells impart fine gradations to the printed paper by variation of depth for each cell. In the gradations, deep cells represent dark portions in the printed paper. The printing ink filled in the deep cells flows over the cells and produces waveform patterns on the printed paper surface. This is usually called "mottling" phenomenon. The waveform patterns produced by the "mottling" phenomenon make the printed surface quite awkward in appearance. Highlight portions of the printed image are printed by shallow cells of the plate. The ink of these portions is over-scraped off or they are not sufficiently filled with ink so that the printed surface of paper will have uninked portions remained on the printed paper. This phenomenon is called "speckle." Both the abovementioned phenomena would cause damage to the appearance of the printed paper. Despite endeavors made for improvement of the process, these drawbacks have not yet been overcome to the advantage of the gravure printing. Such drawbacks are particularly apparent in the gravure printing of postage stamps which particularly requires beauty and a good quality product. Additionally, this gravure printing is not available for preventing forgery.
There is also a high grade printing process such as the overlapping printing process which combines the advantages of described gravure printing and the engraving printing. However, this printing process is technically hard because the two processes must be separately undertaken. Therefore, full conformity of printing or perfect register of the printed product are not obtained.
It is a primary object of the invention to provide an improved process of intaglio printing which can serve for the prevention of forgery substantially for any kind of securities. The process for printing in accordance with the present invention comprises steps of producing patterns, portraits, or drawings through fine and delicate engraving on the gravure plate, imparting various colors on the different portions of the gravure plate with desired ink, whereby one-plate multicolor printing which is unable to obtained by conventional gravure printing can be readily attained on this gravure plate. The process makes it possible to print any kind of bank notes, postage stamps, bonds and securities being fully prevented from forgery or counterfeiting furnished.
Another object of the invention is to produce a useful printed paper which is free from "mottling" or "speackle" by use of the gravure plate.
Another object of the invention is to obtain a printed paper with photographically rich gradations that cannot be singly achieved by prior art engraving intaglio printing.
It is a further object of the invention to obtain a printed paper which has printed surfaces in perfect register not heretofore provided by overlapping printing in combination of gravure printing and intaglio printing.